Microcircuit electronic products are typically assembled from individual components assembled into "packages". In practice individual components are "picked" and "placed " on a substrate. Substrates may be flexible polymer films or rigid ceramic pieces. Substrates may have multiple layers of circuit traces with interconnections between layers made in the "Z" direction through vies. Some components can be directly electrically attached to pads on the substrate with solder or adhesive or the like. Other components have connection pads that do not lie in the plane of the surface of the substrate. To accommodate the "height" of these pads, a technique such as wire bonding is used to route signals between the pads that lie in different planes.
For example it has been common practice to glue or solder integrated circuits to a ceramic substrate and then to make circuit interconnections with "wire bonds" between pads on the integrated circuit (IC) and a pad on the substrate. The "wire bond" is a small loop of wire that leaves the pad on the IC and loops over the edge of the IC and drops to the surface of the substrate. Wire bonds are rapidly stitched onto the IC during production and a typical throughput is 5 wire bonds per second. Both vie and wire bonds form acceptable signal paths for the package as long as the signal of interest is "low frequency".
However, wire bonds both attenuate and radiate signals in the low gigahertz range. The wire itself has a parasitic inductance, which becomes a significant circuit element in the gigahertz range. The conventional solutions to reducing the attenuation have included both "wedge" bonding and "ribbon bonding". Both of these techniques are efforts to reduce the length of the wire and therefore to reduce the inductance of the "wire".
In the wedge technique, the wire is routed at an acute angle off the pads to minimize the total length of the connection. Such connections can be made at a rate of approximately 2-3 bonds per second. Ribbon bonds substitute a flat ribbon wire for the conventional circular cross section wire of wire bonding. The ribbon has a parasitic capacitance, which is large with respect to the inductance, which minimizes attenuation. However successful ribbon wire bonding is critically dependent on component placement. This process is also extremely slow.
A similar signal routing problem arises on the substrate itself. In a multi-layered substrate linear signal traces typically lie close to a ground plane. As a consequence signal paths can be designed with a constant nominal impedance using well known "stripline" techniques for RF signals. However if the signal path departs from the stripline path and passes in the Z direction then the asymmetry creates an impedance mismatch with an associated attenuation and reflection. Ceramic substrates are particularly prone to this problem because they are brittle and additional thickness in the z-axis is required for mechanical strength. The increased thickness and high dielectric constant exacerbates the impedance mismatch problems.
Consequently there is a need for improved interconnection devices and methods for production of high performance high frequency circuitry "packages".